The regulation of wireless today is based on a fixed spectrum assignment policy where government agencies regulate spectrum usage and assign portions of the spectrum over extended periods of time and covering large geographic areas to licence holders or for certain services. Large portions of the allocated spectrum are utilised intermittently and spectrum use is congested at particular regions of the spectrum space while a considerable part of it is left underutilised. The inefficient use and scarcity of spectrum has demanded the adoption of a new paradigm in wireless communication where the available wireless spectrum is exploited opportunistically.
The radio frequency spectrum is the range of frequencies from 3 kHz to 300 GHz. This spectrum is a finite resource that is used for wireless communications and services. As a finite resource, it is important that it be used and managed carefully. Demands for wireless communication in consumer electronics and personal high data rate networks are continuously increasing, as have quality of service requirements in terms of throughput, reliability and availability of wireless services [1]. It is expected that there will be a considerable increase in the number of devices making use of different wireless standards and technologies in the future. On the one hand there will be greater provision and access to broadband multimedia services but on the other hand getting multiple heterogeneous radio systems to coexist harmoniously in shared spectrum is challenging. Traditionally, network operators have mostly been privileged to have exclusive rights to access parts of spectrum assigned to them and hence the problems of coexistence and limited spectrum could be ignored. At present however, it has become necessary to use spectrum more efficiently so as to facilitate the further growth of wireless communication and the future knowledge economy and information society.
Fig. 1: South Africa frequency allocations chart – 2014 RC1. (Click on image to enlarge view)
Access to spectrum and regulation
Access to radio frequency spectrum is regulated by designated regulatory authorities that determine how certain spectrum bands can be used and provide certain rights to licensed and unlicensed users. These regulatory authorities make decisions in the public interest with the aim of enhancing societal benefit, safety and general welfare. Part of their mandate includes defining regulatory rules constraining access to radio frequency spectrum as part of a spectrum licensing regime. Such regulation is necessitated by the fact that radio spectrum is a finite publicly available resource that can be used for a multitude of services which may create undesirable effects to one another if not coordinated well. For example, radio telescopes such as those used in the Square Kilometer Array (SKA) project are used in astronomy to observe celestial objects in the observable universe. Should the same radio frequencies used for radio astronomy be used by another service close to the telescopes then interference may be created which can detrimentally affect the quality of the scientific observations. Such a problem exists with other types of wireless services where there is the emission of electromagnetic radiation at radio frequencies which may result in radio frequency interference; regulation of radio spectrum mitigates undesirable effects like these and makes reliable and efficient spectrum use possible.
Licensed and unlicensed spectrum
Licensed
Licensed spectrum is the part of the radio frequency spectrum that is allocated to some radio services for exclusive use. Licensed spectrum can be accessed for exclusive access or shared access of the same type of radio service. Licence holders usually pay a fee for these spectrum access rights and get protection from unwanted interference from other radio systems. Licensed spectrum is very valuable because of the benefits it provides as well as the problem of spectrum scarcity, as such licencees charge their customers to use it and make financial profits. Licencees are required to ensure that certain conditions are met such as the use of a particular transmission technology and reaching a certain fraction of the population within a given time period. The sale of spectrum licences often takes place by way of auctions. It is a very expensive process due to the time and difficulty involved. Underutilised or unused spectrum cannot be used if a licence has been taken out for it which leads to spectrum inefficiency. Licences typically expire after a decade with the option of being renewed.
Unlicensed
Some parts of the radio frequency spectrum are reserved as unlicensed spectrum and are open for inclusive use. Despite this, unlicensed spectrum is still stringently regulated with usage of the spectrum being permitted provided wireless communication devices meet the specified technical rules or standards put in place to limit possible harmful interference arising from the transmission of other devices. Flexibility is provided in terms of usage rights and there is no particular method of accessing spectrum that is defined or mandated. The most common licence-exempt band is the industrial, scientific and medical (ISM) band between 2400 MHz and 2483,5 MHz. The success of technologies such as WiFi and Bluetooth in the licence-free ISM band is evidence of the economic advantage of unlicensed spectrum and shows that it is possible to use spectrum more efficiently than is typically the case in licensed bands.
Spectrum scarcity, real and artificial
In order to guard against interference from other radio systems, a wireless service provider can licence spectrum for exclusive use from the regulatory authority. As more and more spectrum gets licensed, a problem of spectrum scarcity arises as there will be less and less spectrum available to licence. This scarcity of spectrum is however in some cases artificial. There are several reasons for this, the first of which is that some licensed radio services and systems may suffer an economic failure resulting in the licensed spectrum not being utilised. An example of this is WiMAX which appears to not have taken off commercially. Spectrum for WiMAX has been allocated and licensed in many countries but network operators appear not to be using it. Unless WiMAX spectrum usage picks up, it is largely wasted spectrum. A second reason for artificial spectrum scarcity is that some spectrum is reserved for occasional military radio and public safety use. This spectrum may be used only rarely. Advances in technology are the third reason why there can be artificial spectrum scarcity. Recently there has been the migration of television broadcast from analogue to more efficient digital broadcast. This has resulted in less spectrum being required to provide the same service. As a result of these reasons, some of what can be considered as spectrum scarcity is actually due to inefficient use of spectrum. All this while the demand for additional spectrum is rising faster than the rate at which new technology has increased spectrum efficiency.
In unlicensed spectrum bands such as the ISM band however, it is common to find multiple heterogeneous radio systems operating in overlapping spatiotemporal regions. There is notable spectrum congestion in such unlicensed bands and the scarcity of spectrum in such cases is real. It has been established that usage of spectrum in assigned bands varies temporally and geographically between 15% and 85% [2]. It is desirable to come up with new methods of spectrum access that can result in more efficient spectrum usage and alleviate spectrum congestion in certain bands.
Guiding principles and approaches to regulation
Approaches
There are four basic approaches to regulating spectrum covering licensed and unlicensed spectrum [3]. The first approach is licensed spectrum for exclusive usage. In this approach a licensee has exclusive and transferable rights for certain spectrum bands. This is used for example in mobile telecommunication. The regulator enforces and protects usage of the spectrum.
The second approach is licensed spectrum for shared usage. Here, access is restricted to a particular technology. Examples include the use of digital enhanced cordless telecommunication (DECT) in Europe and public safety services.
A third approach to regulation is unlicensed spectrum. In this approach open access is granted to all radios that function in accordance with certain spectrum etiquette rules from the regulator. There is no privilege for interference protection in licence-exempt spectrum. WiFi and Bluetooth are examples of technologies that operate using unlicensed spectrum. There is a fourth approach that can also be followed which is that of open spectrum where anyone can access whatever spectrum band with no restrictions subject to a minimal collection of guidelines required for spectrum sharing from technical standards or accepted etiquette.
Guiding principles
Six objectives of spectrum access standards that are influenced by regulation and need to be balanced are as follows.
Quality of service (QoS): Adequate QoS must be possible for all radio systems according to their applications.
Availability: A radio should not be denied access to spectrum and transmission for extended period of time.
Innovation promotion: Innovations in fast changing and economically successful and wireless communication markets must not be impeded by spectrum regulation.
Efficient use: There must not be wastage of spectrum and there must be high spatial reuse of it.
Dynamic use: The existing local radiofrequency environment and spectrum usage policies must be taken into consideration so as to use spectrum in an adaptive and dynamic way.
Cost effectiveness: Radio regulation must not increase the costs of commercial wireless communication devices as a result of the techniques required by regulation.
Regulatory authorities worldwide
Globally
Regulation of spectrum usage is done by national and international institutions. These regulators licence spectrum for exclusive or shared usage in a process known as spectrum allocation or frequency allocation. It is necessary to harmonise the process of allocating spectrum globally and this is done with the assistance of the Radio communication sector of the International Telecommunication Union (ITU-R) which is an agency of the United Nations. The ITU-R endeavours to guarantee efficient, equitable, rational and economical radiofrequency usage by all wireless communication services. Agreements of the ITU in spectrum allocation are found in the ITU Radio Regulations (ITU RR). These agreements have treaty status and regulate radio frequency spectrum usage internationally. These also provide a common framework for national and regional planning. Every three to four years there are World Radiocommunication Conferences (WRCs) at which the ITU RR are revised.
South Africa
In South Africa the regulatory authority is the Independent Communications Authority of South Africa (ICASA). Historically this has not always been the case, before 1994 operators themselves such as SABC for broadcasting and Telkom for telecommunications were responsible for managing spectrum. Independent management of spectrum began after the passing of the Independent Broadcasting Authority Act (Act no 153 of 1993) which paved the way for the establishment of the Independent Broadcasting Authority (IBA). The South African Telecommunications Regulatory Authority (SATRA) was established after the passing of the Telecommunications Act (Act no 103 of 1996). IBA was responsible for the regulation of broadcasting whereas SATRA regulated telecommunication. ICASA was established in July 2000 and merged SATRA with IBA. ICASA was formed as a result of the Independent Communication Authority Act of South Africa Amendment Act (Act no 13 of 2000). The ITU has divided the world into three different regions for the purpose of allocating frequencies and South Africa falls into ITU region 1. ICASA as a result aligns its frequency allocations with those of ITU region 1 in the ITU RR.
Other countries
Each country has its own regulatory bodies governing spectrum usage. In the United States of America (USA) the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA) are responsible for regulating spectrum. The FCC handles non-governmental use of spectrum whilst the NTIA looks at spectrum used by government. In Europe the Electronic Communications Committee (ECC) of the European Conference of Post and Telecommunications Administrators (CEPT) is responsible for regulation. CEPT has 48 member countries as of 2014 each of which generally realise what the ECC decides. Matters relating to spectrum allocation are attended to by the frequency management working group whilst radio regulation and spectrum engineering issues are attended to by other coordinating committees. The Office of Communication (Ofcom) is the body mandated with the regulation, assignment, licensing and management of radio spectrum in the United Kingdom (UK).
In Japan, the Ministry of Internal Affairs and Communication is the regulatory authority whilst in China the role is filled by the Ministry of Information Industry at a national level and local radio regulatory authorities at the provincial level.
Radio frequency plan in South Africa
The chart accompanying this article shows how frequency is allocated in South Africa as contained in the National Radio Frequency Plan [4]. In some cases once spectrum has been allocated it is necessary to undergo a process of radio frequency migration. Radio frequency migration is defined as “the movement of users or uses of radio frequency spectrum from their existing radio frequency spectrum location to another” [5]. This can happen when a change in the use of a radiofrequency band is needed so as to harmonise the South African National Radio Frequency Plan with the ITU-RR or the final acts of the most recent WRC. Another cause can be harmonisation with the frequency allocation plan of the Southern African Development Community (SADC). In some cases ICASA can determine that a change in the use of a spectrum band is needed to enable more efficient spectrum usage or meet legal objectives. The regulator can also decide that the assignment of frequencies within a radiofrequency band to a certain spectrum licensee needs to be changed to provide for greater efficiency in the use of spectrum which also results in r adiofrequency migration. Related to spectrum migration is spectrum re-farming which is defined as “the process by which the use of a radiofrequency spectrum band is changed following a change in allocation, this may include change in the specified technology and does not necessarily mean that the licensed user has to vacate the frequency”. Two South African Band Re-planning Exercises (SABRE) were carried out in 1997 and 2001. These were followed by two national radiofrequency plans in 2004 and 2010. Subsequent to this the National Frequency Migration Plan of 2012 and National Radio Frequency Plan of 2013 was developed.
Dynamic spectrum access
The inefficient use and scarcity of spectrum has resulted in a push for the adoption of flexible spectrum access policies by radio frequency spectrum regulatory bodies. Optimal spectrum usage can be realised through the use of the concept of dynamic spectrum access (DSA) where network licences and priorities are not set at design time but rather radios are allowed to negotiate use of spectrum locally for a given time window. A first step to realising DSA is opportunistic spectrum access (OSA) where radios can search for unused spectrum in licenced bands referred to as white spaces or spectrum holes and proceed to use them.
OSA can be realised using a new technology known as cognitive radio (CR). CR technology is a revolutionary communication paradigm that has emerged in recent years that can be used to mitigate interference and enhance reliability in a heavily congested wireless network. A formal definition of a cognitive radio is: “Cognitive radio: A radio or system that senses its operational electromagnetic environment and can dynamically and autonomously adjust its radio operating parameters to modify system operation, such as maximize throughput, mitigate interference, facilitate interoperability, access secondary markets”. Long established methods of sharing spectrum make the assumption that radios in a network collaborate categorically in an unchanging environment. In cognitive radio networks however, interactions with other users and the dynamic environment must be taken into account in order to adapt the operational configuration.
References
[1] L Berlemann and S. Mangold. “Introduction,” in Cognitive Radio and Dynamic Spectrum Access, 2009, . DOI:
10.1002/9780470754429.ch1.
[2] I F Akyildiz, W. -. Lee, M. C. Vuran and S. Mohanty. NeXt generation/dynamic spectrum access/cognitive radio wireless networks: A survey. Computer Networks 50(13), pp. 2127-2159. 2006.
[3] L Berlemann and S. Mangold. “Radio spectrum today – regulation and spectrum usage,” in Cognitive Radio and Dynamic Spectrum Access, 2009, . DOI: 10.1002/9780470754429.ch2.
[4] ICASA, “National radio frequency plan 2013,” Government Gazette Republic of South Africa, Tech. Rep. 36336, 2013.
[5] ICASA, “Draft frequency migration regulation and frequency migration plan,” Government Gazette Republic of South Africa, Tech. Rep. 35598, 2012.
Contact Tapiwa Chiwewe, CSIR, Tel (012) 841 2285, tchiwewe@csir.co.za
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